Cathode ray tube screen



Dec. 5, 1939. I M. PLQKE y2,182,451

CATHODE RAY TUBE SCREEN Filed Jan. 21. 1958 s sheets-sheet 2 PICTURE SCREEN Dec, 5, 1939. 4M. PLoKE cATHoDE RAY TUBEscRE`EN Filed Jan. 21, 1938 Sheets-Sheet 3 Patented Dec. s, 1939 cA'rnonE RAY TUBE sonEEN Martin Plolxe,v Dresden, Germany, assigner to Zeiss llkon many vAktiengesellschaft, Dresden, Ger- Application January 21, 1938, Serial No. 186,23

. /In Germany January 18, 1937 '1a claims. (cl. 25o-1an The invention relates to improvementsv in amethod of light control in cathode ray tubes,

particularly for television purposes.

It has been proposed heretofore in the television art to employ light control methods which are based upon the thermic effect of the electron bombardment and in which for instance, a metallic plate arranged in a highly evacuated space was heated to incandescence according to the brightness of the individual picture points. Practical tests, however, disclosed that a considerable dissipation of the irradiated plate occurs, resulting in a very short life of the cathode ray tube.

, It is also diiicult in these known arrangements to produce a suicient large irradiation capacity to heat the plate to incandescence.

The principal object of the present invention is a method of light control for television purposes in which the change in shape of conductive or insulating material, when subjected to heat, is made use of.

In accordance with the invention. a screen composed for instance of a number of reeds, is arranged transversely in the path of the electron beam. The reeds are of such a structure that they change their shape in response to the heating effect of the electron beam and thereby cause a locally diierent shading of the beam of light striking the screen. The light passing through the screen is projected onto a picture screen.

" It is also an object of the invention to employ for the production of the aforesaid reeds a socalled bi-metal composed of two dierent strips of sheet metal welded or soldered together and having each a different coeiiicient of thermal expansion. y

Other objects of the invention will appear from Athe following description of the invention with reference to the accompanying drawings, in

which Fig. 1 illustrates diagrammatically a Braun tube constructed in accordance with the presentv invention.

Figs. 2 and 3 illustrate in elevation and end view respectively one element of the screen within th Braun tube. I Flgs. 4 anddillustrate diagrammatically the eilect' of anelectron 'beam upon two diierently constructed screens,

Fig. 6 illustrates diagrammatically a modified embodiment of a Braun tube. and Figs. 'l and 8 -illustrate in front elevation and side view the screen employed inthe Braun tube of Fig. 6. A,

Referring to Fig. -1 the Braun tube I is pro-- vided with a neck 2 in which are arranged the4 customary means for producing, concentrating and defleoting an electron beam. These means comprise in the illustrated embodiment an in- 'directly heated cathode II,-a control electrode. I2, an anode I3, the lens electrodes' I4 and I5 and the two pairs of deilecting plates I6 and I'I respectively. Thepotentials required for the various electrodes are taken from the potentiometer In the envelope proper of the Braun tube is mounted a screen 3. The same consists in accordance with the present invention of a plu- .rality of parallel' strips 4 mounted on parallel threaded rods 5.y The strips 4 are spaced from 15 each other -a predetermined distance by suitable spacers.v The Figs. 2 and 3 lillustrate one of the strips 4 of the screen 3 -in elevation and end view respectively. It will be noted that each strip 4 x vis provided with a number of transverse slots in 2 one longitudinal edge thereof to produce so a comb-like structure having teeth 6,' each having its free ends curved toward the adjacent lower strip. v

The lens 1 arranged in front of a source of, light' 9 projects a beam of substantially parallel light rays onto the screen 3.' The lightrays passing through said screen areprojected by a lens 8' onto a picture screenIIl, which receives an image of the screen 3. The screen 3 is electrically connected with the anode and. with respect to the" latter is positively charged. The reeds 6 are curved in such manner that when the electron current is zero no light can pass through the screen. Whenan electron beam strikes the screen, however, the curvature of the reeds corresponding to the individual picture points is nulliftied and according to the modulation of the electron beam the screen 3 is rendered locally permeable to light. Theitime period during which the reeds retain their changed shape is governed by the heat conductivity of the reeds.

If the length of the reeds is for instance .2 inch and their thickness is .002 inch, a heating of the reeds of 212 F. is sutllcient to cause a noticeable change in" shape of the bimetallic reeds. The distance of the parallel strips 4 from each other is preferably made equal or approximately equal the width of the reeds, in order to produce substantial symmetric picture points. The total sum of the reeds of the screen 3 should be equal or larger than the number oie the picture points of the television picture. Therefore,

the intended controlling effect will be obtained withthe method of the present invention at conheretofore practiced Since the method of the invention requires a lower irradiation energy the cathode ray tube can be operated with lower potentials, which is another advantage over other thermic methods of the prior art.

Fig. 4 illustrates diagrammatically a point-like illumination of the picture screen arranged directly behind the reed screen. The electron beam, when striking a normally curved reed 6, causes the latter to straighten out and the `light can now pass at this point through the reed screen.

Fig. 5 illustrates diagrammatically a point-like shading of the picture screen. In this mo'diiied arrangement the reeds are normally straight and the light passes normally through all the slots in the reed screen. An electron beam striking a reed will cause the latter to assume a curved shape, thusl causing a point-like shade onthe picture screen. -In this manner the dark values `of the television picture rare controlled. It is hereby .necessary to select the modulation potential of the electron beam so that the maximum electron current appears at the dark spots of the television picture.

According to the invention the metallic reeds may also be blackened and be arranged in front A of a white surface so that the electron beam during scanning produces differently dense shadow on the white surface. In this manner it is possible to observe the television picture in daylight. In the latter case the light reiiectedfrom the screen may be employed for the projection of the picture. l i

As indicated in the Figs. 4 and 5 the reeds B may be supported by the picture screen or may be fused into .a glass plate. A white picture screen is then applied to the glass plate.

' The Figs. 6,- 7 and 8 illustrate a. modified arrangement of the invention. While the meansl for producing, concentrating and defiecting the electron beam are the same as in Fig. 1 and therefore designated with similar reference characters, the reed screen 381s of different construction. It consists of a glass plate 2| provided with a smaller number of reeds 6, preferably of just a sumcient number necessary for one line .50 of the picture. 'I'hese reeds are repeatedly swept over by the electron beam. The light passing thereby through this single line is projected by the lens 8 onto a rotating mirror i9 or a mirror wheel, which in turn reflects the light onto the 55 picture screen 20 upon 'which the picture is assembled line by line. This arrangement has the advantage that the construction of the treed screen is much simpler, since only reeds for one lineare necessary. The mirror wheel I9 has to m be arranged in such a manner and hasto be rotated with such a speedthat each mirror of the mirror wheel assembles one picture'.

In this embodiment of the invention also a substantial gain in brightness is obtained com- 05 pared with those television methods which are based upon the deflection and control of a single light point.

According to the Figs-- 7 and 8, the reeds 6 are fsed into the glass plate 2|.l The rear ends of 70 the reeds which project from the rear face of the glass plate 2| are provided with conductive strips 22 tor `o'nduct the heat away from the ,l reeds. y Itis also contemplated to provide other means 75 for conducting the heat away' from the reeds.

aissfisf Preferably the time constantof the fading away of the change in shape is selected so that within the period of a 'picture change the deformation of the reeds returns to zero. It is also possible to cool the supporting structure of the reed screen and if desired the Asupporting means structure may be extended through the wall of the tube Aenvelope and thus increase the dissipation of the o Aing means for producing a cathode ray beam, particularly for television. a screen upon which said beam is focused, said screen being capable of 2( transmitting light under cathode ray bombardment in amounts proportional to the intensity of the ray, said screen comprising a plurality of bimetallic reeds mounted in a single plane and extending each substantially at 'a right angle to 25 said plane, said reeds being deformed momene.

, tarlly when being struck by the cathode ray beam.

2. In a cathode ray tube of the type containing means-for producing a cathode ray beam, particularly for television, a screen upon which said 3.0 beam is focused, said screen being capable of transmitting light under cathode ray bombardment in amounts proportional to the intensity of the ray, said screen composed of a plurality of spaced parallel bimetallic strips having one of 35 ytheir longitudinal edges slotted to`form a comblike structure, said strips being mounted in a singie plane so that the teeth of the comb-like structures extend substantially at right angles to said plane. the teeth of said comb-like structures being 40 adapted to be deformed momentarily by the heat of the cathode ray beam striking the said teeth.

3. In a cathoderay tube of the type containing means for producing a cathode ray beam,

`particularly for television, a screen upon which 45 said beam is focused, saidscreen being capable of transmitting light under cathode ray bombardment in amounts proportional to the intensity of the ray, said screen comprisig a plurality of bimetallic reeds mounted in a single plane and extending each substantially at a right angle to said plate, said reeds being deformed momentarily when being struck by the cathode ray beam, the total numbers of said reeds in said screen being at least as large as the number of picture points in one line of the picture to be reproduced.

4. In a cathode ray tube of the typecontainlng i means forproducing a cathode ray beam., particularly for television, a screen'upon which said beam is focused, said screen being capable of transmitting light under cathode ray borlbardment in amounts proportional to the intensity of the ray, said screen comprised of a plurality of spaced parallel bimetallic strips having one of their longitudinal edges slotted to form a comb- 35 like structure, said strips'being mounted in a single plane so that the teeth of .the comb-like structures extend substantially at right angles to said plane, the teeth of said comb-like structures beingadapted to be deformed momentarily by the heat of the cathode ray beam striking the said teeth,. the total numbers of teeth in said screen being at least as large as the number of picture points in the picture to be reproduced.

5. In a cathode ray tube of the type containing 'l5 means for producingv a cathode ray beam, particularly for television, a screen upon which said beam is focused, said screen being capable of" mentarily bythe heat of the cathode ray beam,

striking the said teeth.

6. In a cathode ray tube of the type containing means for producing a cathode ray beam, par- '20 ticularly for television, a .screen upon which said beam is focused, said screen beingcapable of transmitting lightunder cathode ray bombard-y ment in amounts proportional to the intensity of the ray, said screen composed of a plurality of 25 spaced parallel bimetallic strips having one of their longitudinal edges slotted to form a comblike structure, said strips being mounted'in a single plane so that the teeth ofthe comb-like structures Iextend substantially at right angles 30 to said plane, the distance between each two parallel bimetallic strips being substantially as great as the width of one tooth, the total numbers of teeth in said screen being at least as large as' the number of picture points ofthe picture to be 88 reproduced, the teeth of said comb-like structures being adapted to be deformed momentarily by the heatof the cathode ray. beam striking the said teeth.

, '1. 1n a cathode ray tube of the type containing o means for producing a cathode ray` beam, particularly for television, a screen upon which said beam is focused, said screen being capable of transmitting light under cathode ray bombardment in amounts proportional to the intensity 5 of the ray, said screen comprising a white picture screen and in front thereof .a plurality of bimetallic reeds extending substantially at right angles'to` said picture screen, said reeds being blackened and being adapted to be deformed momentarily by the heatof the cathode ray striking the said reeds, thereby causing 'locally different shadings of a beam of light projected onto the front face of said picture screen.

8. In a cathode ray tube of the type containing meansfor producing a cathode ray beam, particularly for television, a screen upon which said beam is focused, said screen being capable of transmitting light under cathode ray bombardment in amounts proportional to the intensity of 60 the ray, said screen comprising means forming a white picture screen, and a plurality of bimetallic reeds attached to said picture screen means and extending kat right angles thereto, said reed being blackened .and being adapted to be deformed momentarily by the heat of the `cathode ray beam striking said reeds,` thereby causing locally different illuminationof the said picture screen by a beam of light projected through said plurality ofreeds onto the said white pictureI beam is focused, said screen being capable of- 15 transmittinglight under cathode ray bombardment in amounts proportional to the intensity of the ray, said screen comprising means forming a white picture screen, and a plurality of bimetallic reeds attached tosaid picture screen means and extending at right angles thereto, said reeds being blackened and normally being straight and when struck by the cathode ray beam assume momentarily a curved lshape at their outer f-ree y. ends, due to the heatv of the cathode ray beam,

thereby causing locally different illumination of the said picture screen by a beam of light projected through said plurality of reeds onto the said white picture screen.

10. :In a cathode ray tube of the type containing means for producing a cathode ray beam, particularly for television, a screen upon which said beam is focused, said screen being capable of transmitting light under cathode ray bombard` ment in amounts proportional to the intensity of the ray, said A`screen comprising means forming a white picture screen, and a plurality of bimetallic reeds attached to said picture screen means and extending at right angles thereto, said reeds being blackened and normally being curved at their free outer ends 'and when struck by the 25 cathode ray beam are straightened 'out momentarily, owing to the heat of the cathode ray beam, thereby causing locally different illumination ofthe said picture screen by a beam of light .projected through said plurality of reeds onto v the said white picture screen,

l1. In a cathode ray tube of the type containing means for producing a cathode ray beam, particularly for television, a screen upon which said beam is focused, said screen being' capable of 35 transmitting light under cathode ray bombardment in amounts proportional to the intensity of the ray, said screen comprising aglass plate and a plurality of bimetallic reeds fused into said glass ,l plate so as to project therefrom at right angles, o said reeds being adapted to be deformed momentarily' by the heat of the cathode ray beam strik-- ing said reeds.

l2. In a cathode ray tube of the type containing means for producing a cathode ray beam, particularly for television, a screen upon -which said beam is focused, said screen being capable of transmitting light under cathode ray bombardment in amounts proportional to the intensity of the'ray, said `screen comprising a glass plate and 50 a plurality. of bimetallic reeds fused into `said glass plate so as to project therefrom at right angles, the total numbers of reeds mounted'. in said glass plate being a't least as large as the number of picture points in one line of the picture to be reproduced, said reeds being adapted to be deformed momentarily by the heat of th cathode ray beam striking said reeds.

13. Ina cathode ray tube of the type containing means-for producing a cathode ray beam, o0.

particularly for television, a screen upon which said beam'is focused, said screen being capable of transmitting light under cathode ray bombardment in amounts proportional to the intensity of theray, said screen comprising a-glass plate, a

plurality of bimetallicreeds fused into said glass plate so as to project therefrom at right angles with both of their ends, the forwardlyprojecting .ends of said reeds being adapted to be deformed momentarily by the heat of the cathode ray beam striking said forwardly extending ends of the reeds, and means attached to the rearwardly pro- .iecting ends of said reeds for facilitating the dispersion of heat from said reeds.

.' PLOKE. Il 

